1. Field of the Invention
This invention relates to an apparatus for mounting an engine to a vehicle body frame in elastically supported condition.
2. Description of the Prior Art
As is well known, an automotive engine vibrates at various frequencies depending on the engine speed. If such vibration is transmitted to the vehicle body without any damping or cushioning, the driver or passengers will feel uncomfortable.
To prevent such a problem, various types of engine mounts have been proposed for mounting the engine in cushioned condition. A typical type of such an engine mount is disclosed in Utility Model Application Laid-open No. 60-64126 or No. 63-95928 for example.
Specifically, the typical prior art engine mount comprises an arm member projecting from an engine, a shell member fixed to the arm member, an insulator made of a relatively soft elastic material and received in the shell member, and a pin inserted through the insulator for fixation to a bracket on a vehicle body frame. Thus, the engine is elastically supported on the vehicle body indirectly through the insulator, so that vibration of the engine is partially absorbed by the insulator before transmission to the vehicle body.
However, the prior art engine mount becomes problematic when the arm member must be made relatively long. Indeed, the arm member is not strictly rigid, and the rigidity of the arm member gradually decreases with increasing length thereof. Thus, the vibration of the engine is transmitted to the shell member as amplified by the inherent elasticity of the arm member, and the amplified vibration is ultimately transmitted to the vehicle body.
Japanese Utility Model Application Laid-open No. 63-142440 discloses the same type of engine mount as described above but which further comprises a special mounting bracket extending from the arm member of the engine for fixation to the shell member, and a dynamic damper mounted on the mounting bracket for reducing vibration of the shell member. The dynamic damper includes a mass member fixed to the mounting bracket via a rubber member. The inertia of the mass member is utilized for counteracting vibration of the shell member.
However, the dynamic damper is effective only in a limited frequency range. In fact, outside the limited frequency range, the dynamic damper amplifies vibration of the shell member due to resonance between the shell member and the dynamic damper. Further, the provision of the dynamic damper requires special configuration of the mounting bracket and the use of the rubber member in addition to increasing weight and mounting space, consequently resulting cost and weight increase.
Japanese Utility Model Application Laid-open No. 63-201824 also discloses a similar engine mount (incorporating an arm member, a shell member, an insulator, and etc.) wherein the arm member and the engine is connected by a vibration preventive stay which has both ends fixedly bolted to the arm member and the engine, respectively. The stay directly prevents excessive vibration of the shell member.
However, because the stay is fixedly bolted to the arm member and the engine, the dimension of the stay must be adjusted on the spot to strictly suit the particular dimensions and configurations of the arm member and engine, so that mounting of the stay is rather troublesome. Further, in case the arm member is made to extend upwardly from the cylinder block of the engine with the stay connecting between the upper end of the arm member and the cylinder head of the engine, dimensional errors of the related components as well as difference in thermal expansion and contraction of the related components will adversely affect the sealing gasket between the cylinder block and the cylinder head. In an extreme case, the gasket may lose its sealing function, thereby leading to combustion gas leakage.